The present invention relates to an improved inductor or antenna for a recognition system, and, more particularly, to an improved inductor or antenna for a recognition system, which system is usable in conjunction with an ignition switch or similar control mechanism for a vehicle or other facility, which inductor or antenna increases the ability of the system to recognize and respond to a key, or similar item, which "matches" the ignition switch or other control mechanism.
Various types of recognition systems are taught by the following commonly assigned U.S. Patents and Applications: U.S. Pat. Nos. 5,287,112; 5,270,717; 5,196,735; 5,170,493; 5,168,282; 5,126,745; 5,073,781; 5,053,774; 5,025,492; Ser. No. 08/021,123, filed Feb. 23, 1993 [TI-17529]; Ser. No. 08/065,286, filed May 21, 1993 [TI-16981]; and Ser. No. 08/086,786, filed Jul. 2, 1993 [TI-17507]. Systems conforming to the teachings of the foregoing documents are marketed under the name TIRIS ("Texas Instruments Register and Identification System"). A recognition system similar in result to, but structurally and functionally specifically different from, TIRIS is disclosed in U.S. Pat. No. 4,918,955. Other types of recognition systems include systems known as AVI (for "Automatic Vehicular Identification"), as taught, for example, by commonly assigned U.S. Pat. No. 5,287,112 and commonly assigned U.S. applications Ser. No. 08/021,123, filed Feb. 23, 1993.
In one type of TIRIS recognition system of interest, a transmitter/receiver (also referred to herein, in the claims hereof and elsewhere as an "interrogator" or a "reader") selectively radiates energy via an associated first inductor or antenna (referred to herein and in the claims hereof as an "inductor/antenna"). The energy is radiated from the vicinity of a key-operated lock, such as a vehicle ignition switch. The radiated energy is often referred to as an "interrogation signal." The radiated energy is received by a second inductor or antenna present on or in a key. The key also includes facilities, such as circuitry (sometimes called a "transponder" or "tag"), connected to the second inductor or antenna. An electrical signal produced or induced in the key's circuitry by the received energy either is affected (e.g., increased or decreased) by the circuitry or effects the generation of a stored, uniquely coded signal by the circuitry. The affected or coded signal is often referred to as a "recognition signal."
Depending on the constituents of the key's circuitry, either the recognition signal is transmitted or reflected back to the transmitter/receiver via the second and first inductors or antennas. A key "matching" the particular ignition switch transmits or causes a predetermined recognition signal. Other keys which operate other ignition switches associated with similar recognition systems may similarly respond to the interrogation signal but transmit recognition signals different from the predetermined recognition signal.
The transmitter/receiver includes facilities which analyze the recognition signals received thereat to determine if the analyzed signal is the predetermined recognition signal produced by the matching key. If the analyzed signal is the predetermined recognition signal, the concurrence of such predetermined recognition signal and the operation of the ignition switch by the matching key starts the engine of the vehicle. If the analyzed signal is not the predetermined recognition signal, either the ignition switch cannot be operated by the key, or, if it can be operated, such operation is ineffective to start the engine.
Portability and/or space limitations usually result in the transmitter/receiver of a TIRIS-type of recognition system being not very powerful. Also, the recognition signals, that is the signals transmitted or reflected back to the transmitter/receiver from the key-included circuitry, may be derived from the limited energy radiated from the transmitter/receiver, not from energy derived from a key-contained power source, such as a battery, as is typical in systems of the AVI type. While the use of a battery with key-included circuitry of a TIRIS system is technically possible, the large size and resulting unwieldiness of the resulting key would probably lead to rejection by users. As a consequence of the foregoing, the key's inductor or antenna and the inductor or antenna of the transmitter/receiver must typically be in close proximity to efficiently electrically couple together the first and second inductors or antennas. Depending on the type of recognition system, such close proximity may range from an inch or a fraction thereof to 18-24 inches.
The keys used with the above type of recognition system may include various types of circuitry, each of which cooperates with an appropriate transmitter/receiver. In a first type of key-included circuitry, wherein the key is a tag selectively removable from merchandise which has been properly purchased, passive components attenuate some electrical value, such as current, which is produced by the energy received in the second inductor or antenna. In effect, the key's circuitry is a load inductively coupled to the transmitter/receiver. A second type of key-included circuitry comprises components which electrically resonate at selected frequencies of the received energy to increase the current produced by the received energy. See, for example, U.S. Pat. No. 4,918,955.
In the foregoing first two types of recognition systems, the attenuated or increased current is reflected or transmitted as a corresponding decrease or increase of energy by the second inductor or antenna back to the first inductor or antenna, where the receiver perceives the resulting recognition signal and compares it to stored data representing the recognition signal which should be produced if the key "matches" the lock.
In the foregoing first type of current-attenuating recognition system, the key's circuitry includes passive components which simply load the transmitter/receiver via the inductive coupling between the inductors or antennas. If the effect of this loading on the transmitter/receiver--for example, a decrease in a signal in the transmitter/receiver which signal is responsible for the energy radiation--is of a selected type and/or magnitude, this fact is detected or measured and analyzed by circuitry in the transmitter/receiver as the recognition signal.
In the foregoing second type of current-increasing recognition system, exemplified by U.S. Pat. No. 4,918,955, the key's circuitry includes plural resonant circuits. The frequency of the energy received by the second inductor or antenna is swept by the receiver/transmitter across a frequency spectrum which includes the frequencies at which the resonant circuits resonate. The increases of the current in the key's circuitry during resonance and the resulting increases in the energy transmitted back to the transmitter/receiver are analyzed by the transmitter/receiver and compared with stored data to determine if the recognition signal has been produced.
A third type of key-included circuitry comprises active and passive components, which in response to the receipt of energy from the transmitter/receiver produce a coded signal. See the above-noted commonly assigned U.S. Patents and Applications. The coded signal, which may be produced by data stored in memory, is transmitted back to the transmitter/receiver, where comparison with the stored "matching" signal is carried out. The coded signal may be produced by modulating a carrier with the stored code, and the carrier may be, or may be derived from, the energy received by the key-included facilities from the transmitter/receiver. In this latter event, the system may be of the TIRIS variety, and the key and its circuitry require no on-board power source and may be said to be "batteryless." This third type of system may also be of the AVI variety, in which case the transponder is typically powered by a self-contained power source.
Recognition systems of the third type may be of the half-duplex variety. That is, after the transmitter/receiver operates in a transmitter mode so that the energy is radiated from the first inductor or antenna to the second inductor or antenna, it ceases operating as a transmitter and operates in a receiver mode to receive and analyze the recognition signal produced by the key-included circuitry. The radiated energy may be modulated RF. The frequency of the carrier radiated by the transmitter/receiver and by the key-included circuitry may be the same or different. Half-duplex recognition systems are disclosed in the above-noted commonly assigned patents and applications except the following applications: Ser. No. 08/021,123 [TI-17529]; Ser. No. 08/065,286 [TI-16981]; and Ser. No. 08/086786 [TI-17507].
Recognition systems of the third type may also be of the full-duplex variety. Specifically, the transmitter/receiver may simultaneously operate as both a transmitter and a receiver, that is, it may simultaneously radiate energy to the key-included circuitry and receive for analysis the corresponding signal produced by such circuitry. Typically, in full-duplex operation, the frequency of the modulated carrier radiated by the transmitter/receiver to the key-included circuitry is different from the frequency of the modulated carrier produced by the key-included circuitry and thereafter received and analyzed by the receiver/transmitter. See above-noted commonly assigned application Ser. No. 08/012,123 [TI-17529].
Recognition systems of the third type may also selectively operate in either a half-duplex mode or in a full-duplex mode depending on which of a variety of key-included circuitry is being utilized. See above-noted commonly assigned applications Ser. No. 08/065,286 [TI-16981] and Ser. No. 08/086,786 [TI-17507].
In prior recognition systems used with a control mechanism such as the ignition switch of a vehicle, the first inductor or antenna may include a coil which surrounds the ignition switch which is connected to the transmitter/receiver. A ferromagnetic core may be interposed between the coil and the switch. The coil alone, or the core+coil constitutes the first inductor or antenna. The physical proximity of the first inductor or antenna to the point of key insertion has been generally expedient, because, as a key containing a transponder is brought close to, and is then inserted into, the insertion point, the core+coil (i.e., the first inductor or antenna) and the second inductor or antenna are physically quite close. As disclosed in above-noted U.S. Pat. No. 4,918,955, such physical closeness may constitute physical engagement of the inductors. Physical closeness efficiently couples the energy radiated from the first inductor to the second inductor.
Several disadvantages have been found by the present inventor to be present in the foregoing type of first inductor or antenna. First, where the first and second inductors are intended to physically contact, as in the '955 patent, failure to achieve such contact may adversely affect the operation of the recognition system. Second, where the first inductor is of the core+coil type as in the '955 patent, but the first and second inductors are not intended to physically engage, as in some of the commonly assigned patents and applications, the energy which is radiated to, and received back from, the key-included circuitry by the core+coil is damped and attenuated by the metal mass of the surrounded ignition switch and its lock. Such damping and attenuation may require large amplification in either the transmitter/receiver or the key-included circuitry, an expensive and potential size-compromising expedient.
Third, the energy radiated by the first inductor or antenna may effect the operation of circuitry included with a second key usable with another ignition switch which is associated with another recognition system. The foregoing may occur, for example, where the user's key ring contains keys used to operate two different automobiles. If the second key is efficiently coupled to the first inductor or antenna, the signals analyzed by the transmitter/receiver will comprise signals from the transponder of the second key superimposed on the signals from the transponder of the first "matching" key. The analysis of the superimposed signals can result in the transmitter/receiver not permitting the "matching" key to operate the ignition switch.
Fourth, ignition switches included in various vehicles may vary in size or configuration. These variations require that there be available first inductors or antennas having cores of varying diameters, as well as a varying number of turns.